SPC AC 281230
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0730 AM CDT SAT MAR 28 2009
VALID 281300Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE
OH/TN VLYS INTO THE SERN STATES...
...SYNOPSIS...
INTENSE UPPER LEVEL LOW WHICH HAS BEEN SLOW TO MOVE OVER OK UP TO
NOW WILL BEGIN TO EVOLVE INTO AN OPEN-WAVE AND EJECT RAPIDLY NEWD
THROUGH TONIGHT INTO THE OH VALLEY. AS THIS OCCURS...SURFACE COLD
FRONT WILL SURGE E-SEWD AND EXTEND ALONG THE CENTRAL APPALACHIANS
INTO THE NERN GULF OF MEXICO BY THE END OF THE PERIOD. LARGE AREA
OF ENHANCED MID AND UPPER LEVEL SSWLY WINDS ASSOCIATED WITH THIS
SYSTEM WILL MAINTAIN ENHANCED DEEP LAYER SHEAR ACROSS NEARLY ALL OF
THE SERN 1/4 OF THE CONUS.
EXTENSIVE DEEP MOIST CONVECTION HAS BEEN PERSISTENT ALONG THE
CENTRAL AND NERN GULF COAST REGION OVER THE PAST 24 HRS...WHICH HAS
INHIBITED GULF MOISTURE RETURN AWAY FROM THE IMMEDIATE COAST THROUGH
THE EARLY MORNING HOURS. HOWEVER...SSWLY LLJ IN EXCESS OF 60 KT
EVIDENT ON MORNING VWP/S OVER THE NERN GULF COAST REGION WILL
TRANSLATE ENEWD ACROSS MORE OF THE SOUTHEASTERN STATES TODAY. THIS
SHOULD ALLOW EFFECTIVE WARM FRONT TO LIFT NWD/BECOME BETTER DEFINED
FROM PORTIONS OF THE CENTRAL CAROLINAS INTO SRN/CENTRAL GA.
LOCATION OF THIS FRONT/INSTABILITY GRADIENT WILL BE PARAMOUNT IN
PINNING DOWN CORRIDOR OF MOST INTENSE SEVERE THREAT TODAY. IN
ADDITION...INTENSE DEEP ASCENT AND STRONG HEIGHT FALLS ALOFT WILL
ROTATE AROUND MAIN UPPER SYSTEM AND SUPPORT CONTINUED THREAT OF
STRONG TO SEVERE THUNDERSTORMS AHEAD OF MAIN SURFACE COLD FRONT FROM
THE MID SOUTH INTO THE TN/OH RIVER VALLEYS. THIS THREAT MAY EVOLVE
IN THE FORM OF SUBSEQUENT BANDS OF MOIST CONVECTION WITH EACH BAND
RACING NNEWD THROUGH THE PERIOD. IT REMAINS POSSIBLE THAT PORTIONS
OF THE SRN APPALACHIANS MAY SEE A RELATIVE MINIMUM IN SEVERE
THUNDERSTORMS AS COMPARED TO REGIONS TO THE NNW AND SSE.
...CENTRAL/NERN GULF COAST INTO THE SOUTHEAST/MID ATLANTIC...
AREAS OF STRONG TO SEVERE THUNDERSTORMS HAVE BEEN PERSISTENT FROM
THE MOUTH OF THE MS RIVER ACROSS SRN AL/FL PANHANDLE DURING THE
EARLY MORNING AHEAD OF MAIN COLD FRONT. STRONG SLY LOW LEVEL FLOW
AND AFOREMENTIONED SURFACE FRONT/INSTABILITY GRADIENT HAS LIFTED NWD
PRECEEDING THIS ACTIVITY...ALLOWING INFLUX OF RICHER MOISTURE TO
SPREAD INTO SWRN GA THROUGH 12Z. THIS TREND SHOULD PERSIST TODAY
AND ALLOW AREA OF MARGINAL TO MODERATE MLCAPE TO EVOLVE FROM THE FL
PANHANDLE INTO SRN GA/ERN CAROLINAS THROUGH THE DAY. EITHER
THUNDERSTORMS WILL ORGANIZE/EVOLVE INTO A MORE COHERENT MCS AND LIFT
ENEWD ACROSS THIS REGION TODAY...OR SERIAL SMALLER-SCALE
SUPERCELLS/BOW ECHOES WILL CONTINUE TO EVOLVE OFF THE GULF AND/OR
NEAR THE FRONT AND IMPACT THE REGION AS THEY RACE NEWD. EITHER CASE
SUGGESTS THIS ZONE COULD BE QUITE ACTIVE WITH A MYRIAD OF SEVERE
THREATS...AT LEAST THROUGH THE EARLY EVENING. NNEWD EXTENT OF
SEVERE THREAT SHOULD BE TEMPERED AFTER DARK...HOWEVER AT LEAST
ISOLATED SEVERE COULD ACCOMPANY STORMS INTO PORTIONS OF THE MID
ATLANTIC DURING LATTER HALF OF PERIOD.
...MID SOUTH INTO THE TN/OH VLYS...
A SEPARATE AREA OF SVR POTENTIAL WILL LIKELY DEVELOP ACROSS PORTIONS
OF THE TN/OH VLYS DURING THE AFTN/EVE...WITH ONGOING STRONG TO
MARGINALLY SEVERE STORMS FROM NERN AR INTO SRN MO. STRONGEST DCVA
WILL TRANSLATE NEWD AWAY FROM THE RICH GULF MOISTURE SOURCE FARTHER
SE. BUT...LINGERING 50S SFC DEW POINTS ARCING BACK ALONG THE
CDFNT/SFC LOW INTO THE LWR OH VLY BENEATH STEEP MID-TROPOSPHERIC
LAPSE RATES WILL CONTRIBUTE TO MLCAPES OF A FEW HUNDRED J PER KG.
MODELS CONTINUE TO SUPPORT SCATTERED TSTM DEVELOPMENT AHEAD OF THE
COLD FRONT THROUGH THE DAY AMIDST STRONG VERTICAL SHEAR....INCLUDING
A FEW LOW-TOPPED SUPERCELLS. LARGE HAIL AND ISOLD DMGG WIND GUSTS
WILL BE POSSIBLE. TORNADOES CANNOT BE RULED OUT...ALTHOUGH FORECAST
SOUNDINGS INDICATE MUCH OF THIS ACTIVITY COULD REMAIN ELEVATED. SVR
THREATS WILL DIMINISH WITH NE EXTENT AND AFTER SUNSET.
..EVANS/GARNER.. 03/28/2009
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